ABSTRACT.-Colonization
of a relatively undisturbed 1915 debris flow by air upper montane Coniferous
forest was examined in Lassen Volcanic National Park in northern California in
1987. Seventy 100-ml circular plots were arranged in four transects across the
flow and sampled to measure tree densities, freights, basal areas and ages. The
composition of the forest changed from a mixture of Abies magnifica, Pinusmonticola and P conforta on steep slopes to a forest dominated by P.
contorta on shallow slopes. This pattern is typical for these terrains at
the 2000-m elevations of' the flow. Age data and historical photographs
indicated little successful colonization before the late 1930s and peak
colonization rates about 1955. Height growth has generally been slow with most
trees being >20-y-(ild but <2-m tall; however, some individuals, including
some recent colonizers, have shown rapid growth. This variation among
individuals suggests (1) that the earliest colonizers are not necessarily those
which will eventually dominate the forest and (2) that opportunities to invade
and occupy the canopy may extend for 30 v after the first successful
colonization.